BOC Signal Acquisition Using Composite Correlation to Eliminate False Lock
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Solution Overview
Problem
Existing satellite navigation systems face challenges in acquiring and tracking Binary Offset Carrier (BOC) modulated signals due to multiple peak autocorrelation functions, leading to acquisition ambiguity and pseudorange errors, especially with cosine BOC signals, and are not effectively addressed by current solutions which often require complex receivers or fail to reject multiple path propagation interference.
Innovation Solution
A method and system for acquiring and tracking BOC modulated codes using a correlation function calculated as wa(τ) = c(τ) − a · [prn(τ + Tc/2) − prn(τ − Tc/2)], where c(τ) is a local replica of the BOC modulated pseudo-random noise code and prn(τ) is an unmodulated pseudo-random noise code, with a weight coefficient 'a' to reduce acquisition ambiguity and improve multiple path rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional acquisition and tracking algorithms are used with BOC modulated signals, then the receiver can process the signal, but acquisition ambiguity and false lock occur due to multiple peak autocorrelation function
Solution Approach 1:
The patent introduces an intermediary signal processing step that combines the autocorrelation function with the cross-correlation function between the BOC modulated signal and unmodulated PRN code. This intermediary combination serves as a mediator to resolve the ambiguity between main peak and secondary peaks, eliminating false lock points while maintaining reliable signal acquisition.
Solution Approach 2:
The patent modifies the test function parameters by incorporating a weighted combination of autocorrelation and cross-correlation functions. By changing the functional form from simple autocorrelation to a composite function involving both autocorrelation and cross-correlation with unmodulated PRN code, the system achieves both reliable acquisition and precise measurement.
2Ease of operation
If Early Minus Late (EML) tracking discriminator is used with BOC(1,1) modulated signal, then code tracking can be performed, but false lock points appear at ±0.55Tc causing pseudorange errors of tens of meters
Solution Approach 1:
The patent introduces cross-correlation with unmodulated PRN code as an intermediary mechanism to identify and eliminate false lock points. This intermediary function provides additional information that distinguishes between true lock at zero delay and false lock at ±0.55Tc, enabling accurate pseudorange measurement while maintaining ease of tracking operation.
Solution Approach 2:
The patent implements a feedback mechanism where the cross-correlation result is combined with the autocorrelation result in the test function. This feedback loop continuously monitors for false lock conditions and corrects the tracking discriminator output, eliminating pseudorange errors while maintaining simple tracking operation.
3Reliability
If cross correlation with unmodulated pseudo-random noise code is used to reduce acquisition ambiguity, then false lock points are reduced, but the receiver complexity increases
Solution Approach 1:
The patent achieves multi-functionality by using the same correlator structure for both autocorrelation and cross-correlation operations. The unmodulated PRN code generator and correlator can serve dual purposes: traditional signal acquisition and false lock detection, thereby reducing receiver complexity while improving acquisition reliability.
Solution Approach 2:
The patent merges the acquisition and false lock detection functions into a single integrated test function that combines autocorrelation and cross-correlation results. This merging eliminates the need for separate processing chains, reducing receiver complexity while maintaining high acquisition reliability and false lock rejection.
4Duration of action of stationary object
If traditional tracking methods are used, then code tracking can be maintained, but multiple path propagation interference cannot be effectively rejected
Solution Approach 1:
The patent introduces cross-correlation with unmodulated PRN code as an intermediary diagnostic tool that enables multiple path rejection. This intermediary function provides additional information about signal authenticity, allowing the tracker to distinguish between direct path signals and reflected multiple path signals, thereby maintaining tracking continuity while rejecting harmful interference.
Data Source
AI summary
A method and a system for the acquisition and tracking of BOC(m,n) modulated codes, m/n equal to an integer, in which a correlation function is calculated of the BOC(m,n) modulated code received from a remote transmitter with a code wa locally generated at a receiver terminal according to one from the following the relationships:wa(τ)=c(τn)−a·[prn(τn+Tc/2)−prn(τn−Tc/2)]wa(τ)=c(τn)−a·[prn(τn+nTc/2m)−prn(τn−nTc/2m)]wa(τ)=c(τn)−a·[prn(τn+nTc/4m)+prn(τn−nTc/4m)]wa(τ)=c(τn)−a·[prn(τn+3nTc/4m)+prn(τn−3nTc/4m)]w(τ)=[prn(τn+nTc/4m)+prn(τn−nTc/4m)]w(τ)=[prn(τn+nTc/2m)−prn(τn−nTc/2m)]wherein c(τ) is a local replica of the BOC modulated pseudo-random noise code with delay τn, PRN(τ) is a replica of the unmodulated pseudo-random noise code, and a is a predetermined weight coefficient, andthe correlation function being at the base of an acquisition test function whereby a code acquisition is recognized for a value of the test function being higher than a predetermined threshold.